Understanding S21 instead of S403 and reason for KRP980b1?

[RaW79]

Hello
it´s kown to me and I´m also using myself a 4 wire connection from a S403 port inside of my Daikin to a faikin module.
But I like to understand a little bit more about the S21-Port and the reason for the two DC voltage supplies (12VDC & 5VDC) on it.

As many of you seems also have analysed the S21 bus signal and therfore seems to have huge experience, can you please explain the reason for this and especially the reason for the KRP980b1 port adapter?

Is this because of low power ability from the 14VDC of the S403 port?

I mean it would be very easy to use a buck converter (5 to 10€) for making 5VDC out of the 14VDC, why therfore is a need for a ~150€ KRP9801b01?

Or are the accessories from Daikin for the S21 port so special that there is this special need?

Thanks for giving me a good hint.

Best regards.